1. Field of the Invention
The present invention relates to optical laser scanning micrometers. More particularly, the present invention relates to optical laser scanning devices and system with improved accuracy.
2. Description of Related Art
Existing laser micrometers have a major short coming of the lack of a spacial filter resulting in allowing slightly off axis reflected and diffracted light being detected coming off of the part being measured. The reason for the problem with existing laser micrometers is a small spot diameter (the diameter of the laser beam) is in range of about 0.1 mm to 2 mm at the measurement area of the passline. From that point the scanning beam diverges to a larger diameter entering the receiver, creating a relatively large spot being focused on the receiver photo diode. The focal point of the scanning laser beam and the focal point of the focused small spot are at two very different distances from the receiver lens. This problem is side stepped, in some products, by designing a relatively collimated beam of larger diameter and of relatively constant size, with a precise long focal length or multi element receiver lens. This arrangement will produce a very small spot diameter allowing use of a small diode reducing off axis light issues. The problem with this type unit is it has even worse accuracy and repeatability short comings than previous devices due to the difficulty of detection of the much larger spot diameter as it scans the parts to be measured at the measurement location. The slightest defects in the transmitter optics, which are impossible to eliminate, will worsen the micrometer's performance even further. Due to the much larger beam diameter at the passline with calibration of the measurement field by a Ronchi rule, a much larger line and gap spacing is needed reducing the number of lookup table values for correction of optical errors between points.
In the 1980s, Lasermike produced a simple mirrored receiver of different detection having short comings including any trace of frame flex affected accuracy and lack of detecting a symmetrical Gaussian laser beam spot shape. It was fairly inaccurate in its measurements. This device involves a laser being shined on a rotating mirror. The scattered light divides in an arc into a collimating lens creating a collimated scanning beam which is utilized to measure the thickness by measuring the missing collimated laser light.